Drop unnecessary exception string casting

This was causing us to drop Service Desk errors (https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/12879) and possibly other important exceptions.

gitlab-org/gitlab#215381 (closed) was closed last year via gitlab-org/gitlab!30268 (merged).

It's hard to be sure we've eliminated all cases since Kibana can't seem to filter out these blank entries (https://log.gprd.gitlab.net/goto/bff4451c43cabf3080d0626d1db36293), but this is all the more reason to get rid of this.